Do not dexpreopt system server jars from updatable modules.

Test: m

Test: The list of updatable system server jars is empty now,
  so I tested that the filer works with a manual experiment:
  - temporarily add ethernet-service to PRODUCT_UPDATABLE_SYSTEM_SERVER_JARS
  - m nothing
  - fgrep -e 'ethernet-service' $ANDROID_BUILD_TOP/out/soong/build.ninja | grep dexpreopt
  - expect empty output (no dexpreopt command is generated)

Change-Id: I0b231e823d5a5a97632daa2b5eb7be3e06782004